"Dry mix" or "no slump" concrete having a relatively low moisture content has been used in the manufacture of concrete pipe in rotary packerhead machines and the like for some time and satisfactory pipe has been thus produced at comparatively high rates of production. Other types of precast concrete products, however, have been conventionally produced employing a "wet mix" casting process. In a wet mix process, the moisture content of the mix is substantially higher than in a dry mix process, and the conventional practice includes the deposition of mix in forms and the subsequent curing of the cast products with the forms in place. Curing may continue for a period of twelve to sixteen hours to reach approximately one fourth the full strength of the concrete and the forms are then stripped from the cast product and the product subsequently aged for a period of fourteen to twenty eight days to reach full strength. While the wet mix casting process has proven generally satisfactory for low volume production, severe drawbacks are encountered in adapting the process to a high volume production operation. The process is inherently slow and a large number of expensive forms are required.
It is the general object of the present invention to provide apparatus for the precasting of concrete products in a "dry mix" process which process and apparatus are particularly well adapted to high volume and low cost production.
A further object of the invention resides in the provision of apparatus as mentioned wherein dry mix is deposited in a casting cavity and vibrated and/or subjected to external pressure whereby to eliminate voids and to compact the mix and to thereby form a green cast product having sufficient initial structural integrity for self support, the product being thus adapted to immediate curing in a free standing condition with its form removed.
A still further object of the invention resides in the provision of apparatus as set forth wherein separable forms of a specific design are provided permitting the use of a single upper form section with a plurality of base form sections and thus effecting substantial savings in the cost of forms.
A still further object of the invention resides in the provision of apparatus as set forth wherein immediate removal of an upper form section upon completion of casting effects substantial reduction in curing time and thereby enhances high volume and low cost manufacture of concrete products.
A still further object of the invention resides in the provision apparatus as set forth wherein sectional form construction with upper and base sections permits the use of the base sections for the post casting transfer of green cast products and the post curing transfer of cured products.
Still another object of the invention resides in the provision of apparatus as set forth wherein forms are provided with sight openings for visually ascertaining the completion of form filling operations, with closure means for filling and thereafter compacting mix in a casting cavity, and with pressure applying and finishing means for compacting dry mix in the cavity.
Still another object of the invention resides in the provision of apparatus as set forth wherein forms are constructed in separable sections so as to provide various sizes of cast products with major portions of the forms usable throughout a range of product sizes.